1. Field of the Invention
The present invention relates to a water base ink for ink-jet recording, an ink-jet recording apparatus provided with the ink, and a method for producing the ink.
2. Related Art
In the ink-jet recording system, ink droplets are formed by using a variety of ink discharge methods including, for example, the electrostatic attraction method, the method in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element, and the method in which bubbles are generated by heating the ink to utilize the pressure generated thereby, and all or a part of the ink droplets are adhered to an objective recording material such as paper to perform the recording. In particular, the ink-jet recording system, in which the mechanical vibration or the displacement is applied to the ink by using the piezoelectric element, is excellent in that the amount of electric power consumption is relatively small, and it is unnecessary to consider the stability of the ink with respect to the heat because no heat is applied to the ink.
Those known as the ink to be used for the ink-jet recording method as described above include those obtained by dissolving or dispersing a variety of water-soluble dyes or pigments in water or a liquid medium composed of water and a water-soluble organic solvent. The ink is required to have the optimum performance characteristics to be used for the ink-jet recording method. Specifically, for example, the following features are required. That is, neither deposition nor aggregation is caused even when the ink is not used for a long period of time. The ink does not cause any clog-up in the ink flow passage or at the tip of the ink-jet head of the ink-jet printer. The printing quality is satisfactory, and the weather resistance is excellent. Neither resin nor metal used for the ink-jet head is polluted.
The ink-jet head of the ink-jet printer, which is based on the use of the piezoelectric element to be used for the system in which the mechanical vibration or the displacement is applied to the ink by using the piezoelectric element, has a structure in which a metal member makes direct contact with the ink in many cases. Specifically, for example, in Japanese Patent Application Laid-open No. 7-195685, stainless steel is used for materials of a nozzle plate and an ink supply plate. In Japanese Patent Application Laid-open No. 10-119263, nickel, which is obtained by the electroforming technique, is used for a material of a nozzle plate. In Japanese Patent Application Laid-open No. 2000-43253, nickel is used for a material of a vibration plate, and stainless steel is used for materials of a chamber plate, a nozzle plate, and an ink supply plate. In Japanese Patent Application Laid-open No. 2002-36545, a nickel alloy steel plate is used for a material for an ink supply plate.
The following problem has hitherto arisen, for example, in the ink-jet head of the ink-jet printer based on the use of the piezoelectric element as described above. That is, when the ink-jet head has the structure in which the metal and the ink make direct contact with each other and especially the ink is a water base ink, then the metal is corroded by the ink and the clog-up and the discharge failure are seriously caused.
The present invention has been made in order to solve the problems involved in the conventional techniques as described above, an object of which is to provide a water base ink for ink-jet recording which does not corrode metal in an ink-jet head provided with an ink flow passage formed of specified metal, an ink-jet recording apparatus which accommodates the ink, and a method for producing such an ink.
According to a first aspect of the present invention, there is provided a water base ink for ink-jet recording which is usable for an ink-jet recording apparatus having an ink-jet head provided therein with an ink flow passage formed of nickel or nickel alloy, the water base ink for ink-jet recording comprising:
a coloring agent;
water; and
a water-soluble organic solvent, wherein:
a current density, which is obtained within an electric potential range of xe2x88x92600 to +300 mV, is not more than 100 xcexcA/cm2 when anodic polarization measurement is performed by using a reference electrode of silver/silver chloride, a counter electrode of platinum, and a working electrode of nickel or nickel alloy.
In the water base ink for ink-jet recording of the present invention, the current density, which is measured under the condition of the anodic polarization measurement described above, is not more than 100 xcexcA/cm2. Therefore, even when the ink is used in an ink-jet recording apparatus provided with an ink-jet head comprising therein a member for constituting an ink flow passage formed of nickel or nickel alloy including, for example, a nozzle plate, an ink supply plate, a vibration plate, and a chamber plate, it is possible to effectively avoid the corrosion of the member as described above. Thus, it is possible to avoid the clog-up and the discharge failure of the ink-jet recording apparatus. In order to avoid the corrosion of the member as described above more effectively, the ink may further comprise benzotriazole.
According to a second aspect of the present invention, there is provided an ink-jet recording apparatus comprising:
an ink-jet head which jets an ink and which is provided therein with an ink flow passage formed of nickel or nickel alloy; and
an ink tank which accommodates the ink, wherein:
the ink comprises a coloring agent, water, and a water-soluble organic solvent; and
a current density, which is obtained within an electric potential range of xe2x88x92600 to +300 mv, is not more than 100 xcexcA/cm2 when the ink is subjected to anodic polarization measurement by using a reference electrode of silver/silver chloride, a counter electrode of platinum, and a working electrode of nickel or nickel alloy. The ink-jet recording apparatus of the present invention is provided with the ink of the present invention which makes it possible to effectively avoid the corrosion of nickel or nickel alloy. Therefore, it is possible to maintain satisfactory ink-jetting characteristics for a long period of time. The ink tank may be an ink container fixedly provided in the apparatus or an ink cartridge which is replaceable.
According to a third aspect of the present invention, there is provided a method for producing a water base ink for ink-jet recording which is usable for an ink-jet recording apparatus having an ink-jet head provided therein with an ink flow passage formed of nickel or nickel alloy, the method comprising:
blending a coloring agent, water, and a water-soluble organic solvent so that a current density, which is obtained within an electric potential range of xe2x88x92600 to +300 mV, is not more than 100 xcexcA/cm2 when anodic polarization measurement is performed for the ink by using a reference electrode of silver/silver chloride, a counter electrode of platinum, and a working electrode of nickel or nickel alloy. More specifically, the blending ratios of the coloring agent, water, and the water-soluble organic solvent and the types of the coloring agent and the water-soluble organic solvent, especially the type of the coloring agent are appropriately selected when the ink is prepared so that the current density, which is measured under the condition of the anodic polarization measurement, is not more than 100 xcexcA/cm2. In particular, it is desirable that benzotriazole is further added to the ink in order to effectively avoid the corrosion of the member for constituting the ink flow passage formed of nickel or nickel alloy.